Arrangement for removing of water in press section of machines for forming a felted pulp web



March 1957 H. N. SKOLDKVIST 2,783,689

ARRANGEMENT FOR REMOVING OF WATER PRESS SECTION OF MACHINES FOR FORMINGA FEL PULP Filed March 26, 1954 WEB 2 Sheets-Sheet 1 INVENTOR.HJSLSKOZcLK u 062; BY

March-5, 1957 SKQLDKVIST 2,783,689

ARRANGEMENT FOR REMOVING OF WATER IN PRESS SECTION OF MACHINES FORFORMING A FELTED PULP WEB Filed March 26, 1954 2 Sheets-Sheet 2 UINVENTOR. HM 61:6 Lei/ll U Lat content is too high.

United States Patent ARRANGEMENT FOR REMOVING F WATER lib PRESS SECTIONOF MACHINES FQR FQRMENG A FELTED PULP WEB The forming of a pulp web in aFourdrinier machine for the production of for instance wallboard plates,carton forming material, mechanical pulp, cellulose filament and thelike is currently made in such a way that a mixture of fiber and waterhas to fiow out onto a moving endless wire cloth. The wire cloth orscreen carrying the mixture will at first run over a number of registerrolls, thereafter over one or more suction boxes, plane or rotating, ora combination of the same and finally through the wet press section. Thepurpose is to extract water successively from the mixture and there byto mat the same to form a pulp web having the lowest possible watercontent. The problem of obtaining a pulp web having the lowest possiblewater content imposes important technical and economical considerations.

After the pulp web is formed it is generally dried in air dryers overcylinder sections or in plane presses, depending upon which fibrousmaterial is being treated and which final product is desired. A pulp webwith a lower content of water will, as a matter of course become cheaperto dry than a pulp web with a higher water content. Besides the economicgain that is attained by working a pulp web with as low a water contentas possible a great many technical advantages are 0 obtained. Forinstance in the pressing of hard wallboard plates in warm presses it mayhappen that it the water content in the pulp web is too high explosionsin the presses may arise. This drawback is avoided if the water contentis maintained below a suitable value. Also water spots will arise on thefinished plates if the water In order to obtain a good forming of thepulp web, the wet lap or sheet, during the manu facture of wallboardandthereby provide great strength in the finished product-one endeavours tomaintain the concentration as low as possible at the flowing in of thefiber mixture onto the wire cloth. Experience has proven that with a lowconcentration of the fibrous mixture, that is, high dilution, asubstantially stronger wallboard is obtained than if the concentrationis high. It is also known that a fine fiber or a one of high grindingdegree or a fine fiber mixed with coarser fiber also considerablyincreases the strength of the finished product.

However, with the present construction of Fourdrinier machines it is notpossible to maintain the desired dilu tion and the degree of grindingthat will give maximum strength in the finished product. If the dilutionand the degree of grinding is as high as desired the machine will notprovide sufficient time for extracting water from the fibrous mixture toobtain the desired water content in the wet lap or sheet at a givenspeed of operation. Of course, if a high dilution, at the forming of thewet lap or sheet and a high degree of grinding, is desired, it ispossible to decrease the speed of the machine in order to attain therequired degree of dryness in the wet lap or sheet when the same leavesthe Fourdrinier machine. However this will result in an undesiredincrease in the capacity of this machine. In order to facilitate theextraction of water from the wet lap or sheet it is possible to increasethe vacuum in available suction boxes or to increase the number of thesame. However in such solution processes there will be the disadvantageof too much wear on the wire cloths or screens so that such a step willbecome economically impossible due to the wear effect on the wire cloth,the interruption of service and other disadvantages. Additionally, toohigh a vacuum may cause the wire cloth to be stuck while the drivingrollers continue to rotate, so that the wire cloth will tear or break.

The press section in the Fourdrinier machine for wallboard of known typeconsists of a number of prepress rolls and behind these one or two pairsof main rolls. Due to the fact that the clearance between the pairs ofrolls through which the wet lap or sheet has to pass decreases in thedirection of movement of the sheet, the same will become successivelycompressed and the water will be extracted. The prepress rolls haveheretofore consisted of smooth, ground steel rollers of smaller diameterthan the main press rolls. The prepress rolls have been separatelyadjustable and the number of pairs thereof has been up to four. Inaddition to the above mentioned endless wire cloth, that passes over thelower rolls there is also provided an endless wire cloth trained beneaththe upper rolls. The formed wet sheet will thereby be confined betweenan upper and a lower wire cloth, thus making it possible to increase thepressing in each step.

The disadvantage of using this construction consists in the fact thatthe water which is expressed out from the fibrous mixture in thecompression zone between a pair of prepress rolls has to pass or flowoff in a direction that is substantially opposite to the direction ofmovement of the Wet sheet. If the compression and thereby the extractionof water in any one step is too great in comparison with a certain speedof movement of the wet sheet and the fiber is for instance desirablyfine ground for the purpose, the extracted water will obtain such highspeed relative to the wet sheet and so high a pressure that the mattingin the sheet is damaged and a crushing effect arises. The risk ofcrushing thus limits speed of the extraction of water to a given speedof the machine. If the speed of the machine is fixed to maintain acertain production and the dryness in the wet sheet is fixed to acertain value, in order to obtain a sufiicient extraction of waterwithout risk of crushing it is necessary to control the dilution and thedegree of grinding accordingly, i. e. the dilution and possibly thedegree of.

grinding has to be decreased. This results, however, as previouslypointed out, in a finished product of an inferior quality. If on theother hand a certain high dilution and degree of grinding has to bemaintained, the speed of the machine has to be decreased to a value thatfor a certain dryness of the wet lap or sheet does not involve any riskfor crushing. In order to force the extraction of water from the wetsheet as much as possible it has been necessary to arrange in front ofthe press section a plurality of rotatable or other suction boxes ofconventional type and in addition thereto one has been compelled tomaintain too high a vacuum in the same resulting in a considerable wearon and short time in the useful life of the wire cloths. That which ismentioned above in connection with the manufacture of wallboard is alsofundamentally applicable for the manufacture of carton forming material,mechanical pulp an cellulose filament. w.-

The purpose of the present invention is to avoid 0 above mentioneddisadvantages in the press section of V a machine that forms a feltedpulp web, wallboard, carton oneness forming material, mechanical pulp,cellulose filament and the like, when the water from the pulp web duringits movement between the prepress rolls is successively extractedbetween an upper and a lower wire cloth. The invention is principallycharacterized in the fact that the compression of the pulp web is soarranged that the water is extracted in the compression zone, higher orlower, or under vacuum in combination with pressure air or withoutvacuum, is removed at right angles or substantially at right angles tothe direction of movement of the pulp web. I t has been proven that thevacuum, which has to be maintained in the purality of suction boxeswhich are required for a given relation in a Fourdrinier machine ofknown type, is 2 to 5 times higher than in a machine in accordance withthe invention. In addition the number of suction boxes has beendecreased to or less than those heretofore required.

These and other characteristic features of the invention will beexplained more in detail in connection with the following description ofillustrated embodiments of the invention. In the drawings:

Figure 1 is a side view of the known arrangement of a press section in aboard forming machine, while Figure 2 isa side view of a press sectionconstructed in accordance with the present invention.

Figure 3 diagrammatically illustrates the action during compression of awet sheet between the prepress rolls, of known performance.

Figure 4 diagrammatically illustrates the action during compression of awet sheet between prepress rolls made according to the invention.

Figure 5. illustrates the action during compression of a wet sheetbetween prepress rolls of another embodiment of the invention.

Figure 6 is a cross section taken along lines 66 of Figure 4 and Figure7 is a cross sectiontaken along lines 77 of Figure 5.

In the embodiment according. to Figure 1, there is shown the knownarrangement of apress section in a board forming machine. The upperprepress rolls are designated at 1 and 2 designates the lower prepressrolls. The numerals 3 and 4 designate the upper and 5 and 6 the lowerrolls in the main press-section. Over the lower prepress rolls 2 and thelower main rolls 5 and 6 runs a wire cloth 7 and under the correspondingupper rolls runs a wire cloth 8. In front of the press section, in thedirection of movement of the wire cloth'7, there is provided a wet sheetorpulp pressing arrangement consisting of two upper rolls 9and'10bearing against the pulp vcb and two lower rolls 13 and 14 journalled insuction boxes 11 and 12. In front of-the rolls? and 13 in the directionof movement of the wirecloth! there are provided two suction boxes 15and 16 equipped with rotating rubber bands.

In the embodiment according to the invention, which is illustrated inFigure 2, the upper prepress rolls are designated at 17 and the lowerprepress rolls at 13. The last mentioned rolls are journalled in suctionboxes 19. In this embodiment the main press consists of one pair ofrolls 2%), 21, but can of course also consist of two pairs of rolls.Similarly as in the above decribed known embodiment a wire cloth 7 runsover the lower prepress rolls and the lower main roll and a-wire cloth 8runs under the correspondingupper rolls. In front of the prepresssection, in the direction of movement of the wire cloth 7, there isarranged'a suction box 24 provided with a rotating. rubber band. As willbe seen from Figure 1, as well as from Figure 2, the successive pairs ofrolls in the prepress section are arranged with decreasing clearancebetween upper and lower rolls, in the direction of movement of the wetsheet, whereby in the feeding forward of the sheet between. the pairs'of rolls the same is exposed to a successivelyincreased compres-$1011..

During the pressing of the wet lap or sheet 25 between a pair ofprepress rolls 1, 2 according to the known arrangement, illustratedschematically in an enlarged scale in Figure 3, the water extracted fromthe wet sheet will pass, as indicated by arrows 26, 27, in a directionopposite to the direction of movement of the wet sheet, whereby willarise the disadvantages as to pressure above the atmospheric etc.described above, resulting in that the matting in the wet sheet willbecome damaged and the risk of a crushing effect will arise.

in Figure 4 there is illustrated on an enlarged scale the action in thecompression zone between a pair of prepress rolls made according to theinvention. In this instance water is extracted from the wet sheet 25 thelower roll 18 is provided with a plurality of circular grooves 28,arranged along the circumference of the roll. By this arrangement thewater that is extracted from the wet sheet will be exposed to a vacuuminstead of a pressure above the atmospheric as is the case with thecurrently known arrangement and the water is removed in directionssubstantially at right angles to the direction of movement of the wetsheet as indicated by the arrows in Figure 4. The lower roll is, asalready mentioned in connection with Figure 2, journalled in a box 19,which is under vacuum. Due to this fact the water is sucked away fromthe wet sheet through said grooves 28 in the roll 18. By means of thisarrangement any pressure in the water above the atmospheric is avoided.The cover 29 of the suction box 19 consists preferably of a Bakeliteplate or the like through which is provided an opening from which aportion of the roll 18 protrudes above the plate in order to decreasethe friction effect on the wire cloth 7. In this embodiment, accordingto the invention the upper roll 17 is smooth. In Figure 6 is illustratedthe arrangement of the grooves 28 along the circumference of the roll18.

In Figure 5 there is illustrated another embodiment of a pair ofprepress rolls according to the invention. This form differs from theembodiment according to Figure 4 in that the upper roll 17 is alsoprovided with circular grooves 30 along the circumference of same andwhich grooves permit water forced up through the upper wire cloth 8 tobe removed substantially at right angles to the direction of movement ofthe wet sheet. This embodiment also includes a suction pipe 31 locatedin front of the upper roll 17 and above the upper wire cloth 8, throughwhich pipe, water passing up through the upper wire cloth 8, is suckedaway. The arrangement further includes a pipe 33 and nozzle 32 on theopposite side of the upper roll 17 through which air under pressureflows to force away the water passing up through the upper wire cloth 3.As shown in the drawings, Figure 5', the pipe or header 33 is disposedclosely adjacent the circumference of the upper roll 17 and the nozzles32 have an extent such as to be disposed in the grooves 30 so that theirterminal and outlet ends are closely above the upper wire cloth orscreen 8 in the compression zone. In Figure 7, which is a cross sectionalong the line 77 in Figure 5, there is illustrated the circular grooves30, 28 arranged along the circumferences of the upper and lower rolls.

By building out the prepress roll section with some further pairs ofrolls and suction boxes connected thereto it ought to be possible tospare all or at least part of the suction boxes provided with rotatingrubber bands or other suction boxes of conventional type, wherebybesides the economic gain that is made possible by this arrangementthere is also avoided the danger of fastening of the lower wire clothdue to suction and possible breaking of the same at too high a vacuum.

Consequently by the present invention, among other things, the followingadvantages are attained:

l. The speed of the machine can be increased resulting in an increasedproduction.

2. The concentration of the fibrous mixture can be decreasedresulting ina stronger product.

3.: The-degree of grindingican' be increasedwhich also increases thestrength of the finished pressed product and furthermore improves thephysical properties of the same product for example smoother surfacescan be attained.

4. The consumption of steam in the warm presses following behind or inthe air dryers can be decreased depending upon the lower water content,which is made possible by the arrangement according to the invention.

5. Possibility of eliminating to a great extent the formation of waterspots in the finished product, also contributing to tr e formation of asmoother surface.

6. Risk of explosions in the warm presses is avoided.

The invention is evidently not limited to the now described andillustrated embodiments but the same can be varied in a plurality ofditferent ways within the scope of the invention.

What I claim is:

1. In the pre-press section of a machine for forming a felted pulp Web,such as wallboard, carton forming material, mechanical pulp andcellulose filament, and in which section water is successively extractedfrom the pulp web while the same is moved forward between an upper andlower wire cloth, said pro-press section comprising at least one pair ofrolls resiliently pressed against said wire cloths, said rollsconstituting upper and lower rolls, the lower roll of said pair havingcircular grooves along its circumference, means for establishing waterextracting currents in front of and behind the lower roll whereby waterextracted from said pulp web in the compression zone between said rollsflows into said grooves substantially at right angles to the directionof movement of said pulp web so as to become distributed uniformly alongthe circumference of the lower roll on the front and rear sides thereof,suction means in front of the upper roll and above the upper wire clothand including at least one nozzle directed toward the compression zonebetween the rolls, said upper roll also having axially spacedcircumferential grooves therein, nozzle means above the upper wire clothand directed toward the compression zone between the rolls and locatedon the opposite side of said upper roll from said suction means andmeans for supplying air under pressure to said last mentioned nozzlemeans to force any water penetrating through the upper wire cloth towardthe suction means.

2. Apparatus for extracting liquid from a pulp web comprising a casingincluding opposite spaced front and rear walls and a top having a slottherein, a roll supported in said casing in spaced relation to saidwalls and with a portion of its periphery projecting into the slot, saidroll having axially spaced circumferential grooves therein, another rollspaced above the first roll in parallelism therewith, means for moving alayer of pulp between the rolls comprising spaced upper and lowerstreams with the lower stream engaging said top whereby the rotation ofthe rolls toward one another establishes a compression zone above theslot for squeezing liquid from a layer of pulp, means applying suctionto the casing to establish liquid extracting currents between the opposite front and rear sides of said first roll and said spaced front andrear walls so that liquid extracted from the rear flows into the groovesof said first roll substantially at right angles to the direction ofmovement of the rear whereby the liquid is uniformly distributed alongthe circumference of said first roll along the opposite front and rearsides thereof, said second roll constituting an upper roll and alsohaving axially spaced circumferential grooves therein, suction nozzlemeans in front of the upper roll as regards the direction of movement ofthe layer and above the upper screen and directed toward the compressionzone for sucking away any liquid passing through the upper screen, andnozzle means for supplying air under pressure located above the upperscreen on the opposite side of the compression zone from said suctionnozzle means and directed toward the latter for forcing any liquidpassing through the upper screen toward the suction nozzle means.

3. In a pre-press section of a machine for forming a felted pup web,such as wallboard, carton forming ma terial, mechanical pulp andcellulose filament and in which section water is successively extractedfrom the pulp web while the same is moved forward between an upper and alower wire cloth, said pro-press section comprising at least one pair ofrolls resiliently pressed against said wire cloths, said pair of rollscomprising an upper and a lower roll, each said rolls having axiallyspaced circumferential grooves therein, a casing surrounding said lowerroll and having an opening parallel to the axis of said roll, saidopening being located in the compression zone between said rolls, meanssubjecting the casing to vacuum whereby water extracted from a pulp webmoving through said compression zone flows into the grooves of the lowerroll substantially at right angles to the direction of movement of thepulp web so as to become distributed uniformly along the circumferenceof the lower roll on the front as well as on the rear side thereof,suction means in front of said upper roll and above the upper wire clothand including at least one nozzle directed toward the compression zonebetween the rolls, and means above the upper wire cloth, extending alongthe whole length of said upper roll and located on the opposite side ofsaid upper roll from said suction means and including a plurality ofnozzles directed toward the compression zone and between said rolls, andmeans for supplying air under pressure to said last mentioned nozzles tocooperate with said suction means in forcing any liquid passing throughthe upper wire cloth through the grooves in the upper roll toward thesuction nozzle means.

4. Apparatus as claimed in claim 2 in which said last mentioned nozzlemeans comprise a plurality of nozzles, a header pipe disposed above theupper screen closely adjacent the circumference of the upper roll andsaid nozzles extending from said pipe and having a length such as toterminate within the grooves closely superjacent the upper screen at thecompression zone.

References Cited in the file of this patent UNITED STATES PATENTS1,483,562 Wagner Feb. 12, 1924 1,572,238 Jones Feb. 9, 1926 2,083,817Berry June 15, 1937 2,443,366 Worden June 15, 1948 FOREIGN PATENTS381,819 Great Britain Oct. 13, 1932

